Add Oslo feature freeze to Train schedule

Per [1], Oslo observes feature freeze earlier than most projects in
order to give consuming projects a chance to implement any new
features in Oslo before their feature freeze.  This should be
reflected in the release schedule.

Change-Id: I5dd46957383749290872504d0648d29198e35407
1: http://specs.openstack.org/openstack/oslo-specs/specs/policy/feature-freeze.html

doc/source/train/schedule.rst

@@ -234,3 +234,14 @@ Keystone Feature Freeze
 
 All new Keystone features must be merged by the end of the week.
 
+Oslo
+----
+
+.. _t-oslo-feature-freeze:
+
+Oslo Feature Freeze
+^^^^^^^^^^^^^^^^^^^
+
+All new Oslo features must be proposed and substantially complete, with unit
+tests by the end of the week.
+

doc/source/train/schedule.yaml

@@ -82,6 +82,8 @@ cycle:
   start: '2019-08-26'
   x-project:
     - t-extra-atcs
+  project-specific:
+    - t-oslo-feature-freeze
 - end: '2019-09-06'
   name: R-6
   start: '2019-09-02'